So far cpu_plugin_mem_cbs_enabled() is only called from
TCG, so reduce it to accel/tcg/.
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <5f59c754-44e5-4743-a2dd-87ef8e13eadf@linaro.org>